It is known that the bail-out of the crew of high-performance military aircraft being in a situation of distress is carried out by ejection of the seat or seats (depending on whether the aircraft is a single- or a multi-seater) out of the cockpit which is, at any rate during flight, closed by a transparent lid, for instance of "Plexiglas" shaped along the convenient aerodynamic outline, currently called a canopy. Quite clearly, this cockpit-enclosing canopy constitutes a major obstacle in the way of the ejection seat and, if no precautions were taken in order to eliminate it, the occupant of the seat would violently bang against it and could get injured or killed while smashing it to pieces. On the other hand, one cannot rely upon an opening of the canopy prior to ejection of the seat, not only because this action is uncertain due to possible failure or disablement preventing its operation, but also because such a preliminary step would consume a significant amount of time, entailing a substantial delay in the bail-out procedure, which in certain cases could happen to be prohibitive.
So, it has long been known to disengage the canopy from the fuselage of the aircraft immediately (about one second) before ejection of the seat by pyrotechnical means such as explosive bolts or like releasable ties, in order to jettison the canopy assembly (see British Pat. No. 711,987). But this way of proceeding had to be ruled out because in practice it amounted to replacing one hazard with another one just as dangerous: the ejected seat with its passenger on the one hand and the bulky canopy assembly (sometimes weighing several tens of kilograms) presenting sharp corners and ruggedness on the other hand, were evolving through the air with high-speed ragged movements and close to each other, whence the danger of violent collisions. This was particularly true when the aircraft was spinning or on the ground: in such situations, the aerodynamic effects did not remove the jettisoned canopy out of the pilot's path.
In modern military aircraft still equipped with ejection-seats, the canopy jettisoning solution is therefore ruled out, the canopy being now held in position. But the obstacle it then constitutes in the pilot's way is diminished, immediately prior to bail-out, by means of detonating fuses controlling explosive charges properly distributed and designed for causing disintegration or frangibilization of the canopy so that, when passing through it, only minute scattered remains are encountered, which in principle should not bring about severe injuries, i.e., since they are not normally capable of making their way through the usual protective clothes worn by the members of the crew. A description of such canopy disintegration or frangibilization systems are to be found respectively in U.S. Pat. No. 3,561,703 to Stencel and U.S. Pat. No. 3,729,154 to Deplante, which provide details about the use of pyrotechnical means which are today very currently employed.
The canopy frangibilizing system by pyrotechnics of this latter patent has been widely practised by the Applicant's assignee and has given full satisfaction with regard to the safety of the crews, especially of single-seaters or of the rear compartment of two-seaters the canopy of which extends along the relative wind flow. However the Applicant has discovered that safety could be further improved in the case of aircraft having a plunging canopy in its front portion, notably at the front piloting compartment of two-seaters.
Owing to its very shape, which plunges at the front, this portion of the canopy happens indeed to be subjected, at high-speed flight, to considerable dynamic pressure directed towards the inside of the cockpit and to which it can perfectly resist under normal conditions. In contrast, such is no longer the case when pyrotechnical frangibilization of the canopy occurs, in anticipation of seat ejection: as soon as it becomes frangible at t.sub.o time, this front portion, far from remaining cohesive until passage of the ejection seat through the canopy at t.sub.o +.DELTA.t time, prematurely disintegrates under the action of such dynamic pressure and at once collapses into the interior of the cockpit, projecting its remains in every direction and therefore in part towards the pilot who is still there at this t.sub.o time and during the whole .DELTA.t time interval until he is out.